answer.code: In function ‘int main()’:
answer.code:103:24: error: ‘__gnu_cxx::__alloc_traits<std::allocator<std::set<int> >, std::set<int> >::value_type’ {aka ‘class std::set<int>’} has no member named ‘extract’
  103 |                 pos[h].extract(fx[c]);
      |                        ^~~~~~~